A mild method for effectively removing the fluorenylmethoxycarbonyl (Fmoc) group using sodium azide was developed. Without base, sodium azide completely deprotected N (α)-Fmoc-amino acids in hours. The solvent-dependent conditions were carefully studied and then optimized by screening different sodium azide amounts and reaction temperatures. A variety of Fmoc-protected amino acids containing residues masked with different protecting groups were efficiently and selectively deprotected by the optimized reaction. Finally, a biologically significant hexapeptide, angiotensin IV, was successfully synthesized by solid phase peptide synthesis using the developed sodium azide method for all Fmoc removals. The base-free condition provides a complement method for Fmoc deprotection in peptide chemistry and modern organic synthesis.

Protein glycosylation is one of the most complicated but significant post-translational modifications. Minor alterations in glycan structure can considerably affect the biology of a cell. Therefore, direct monitoring of glycan patterns of glycoproteins is closely related to cancer progression as well as metastasis. In this study, a boronic acid (BA)-tosyl-directed strategy to selectively immobilize glycoproteins on glass slides was successfully developed even in the presence of high-abundant nonglycosylated proteins. To enhance the immobilization efficiency and reduce the undesired nonspecific absorption, the strain-promoted alkyne azide cycloaddition (SPAAC) conjugation chemistry and surface blocking conditions were carefully optimized for the collection of reliable data. The optimized glycoprotein microarray platform describes specific lectin-recognition patterns of glycoproteins of interest in E. coil lysate and fetal bovine serum (FBS), which encourages us for direct monitoring of glycan patterns from human sera without tedious sample preparation. Three serum groups comprised of healthy controls and lung cancer and pancreatic cancer patients were analyzed by this new technique. Remarkably, the distinguishable glycan patterns of the three groups make them a powerful platform for cancer screening and prediagnosis.